1. Technical Field
The present invention relates to a discharge lamp lighting apparatus, a method for controlling the same, and a projector.
2. Related Art
A high-pressure mercury lamp, a metal halide lamp, and other discharge lamps are used as the light source of a projector. In such discharge lamps, discharging causes electrode consumption, which changes the shapes of the electrodes, sometimes resulting in flickering in which the discharge start position abruptly changes. Flickering undesirably changes the luminance of the discharge lamp abruptly and greatly.
To solve the above problem, JP-T-10-501919 discloses a discharge lamp driving method for suppressing flickering by increasing the magnitude of a discharge lamp AC driving current in the second half of the half cycle of the AC driving current.
However, when the method described in JP-T-10-501919 is used to continuously drive a discharge lamp, the temperature at the tip of each electrode of the discharge lamp increases, which may cause excessive evaporation of the electrode material.
Further, it is a known fact that when the method described in JP-T-10-501919 is used to drive a discharge lamp, a protrusion at the tip of each electrode, which is the discharge start point, grows. In this case, the arc length decreases, and the discharge lamp driving voltage decreases accordingly. Since a discharge lamp is driven at constant power in many cases, decrease in the discharge lamp driving voltage may excessively increase the current flowing through a discharge lamp lighting apparatus.